Depends on how cheap an exhaust you can put up with. A budget back box should only be about £35 or so, but the muffling isn't as effective as the better ones. I'm desperately trying to rust my budget exhaust out!

If you can get the back wheels a foot off the ground, you can do it yourself but it's not a fun job. Not technically difficult, just a horrible working position and rusted bolts. Much easier on a ramp.

My rule of thumb on exhausts is, if it's a Classic car it's a DIY job. Good parts are cheaper through the specialists and may not be available at all via the usual outlets.

If it's a modern car, local Tyre and Exhaust centre. It isn't worth the hassle for the minimal cost saving that a DIY approach will yield. Last time was the centre section on a Zafira. Cheapest online price for the part was 115 EUR including VAT. The local Kwik-Fit sold me the same branded part, fitted and including new bolts, mountings etc for 140. 25 EUR to have someone else wrestle with all the rusty clamps? Bargain.

Back box for an Aygo online is a shade over 60 EUR in these parts....

I have just change the rear box myself last night. I have to say some of the opinions on here are not helpful at all, I wish people wouln't give out these opinions when they never left their arm chair.

Firstly I ordered the parts. I got a Klarius rear box from Euro Car Parts (Car Parts Saver) on ebay for £31.80 delivered. Klarius are a big maker of copied parts with a factory in Stoke on Trent and have a good enough name. I got a new clamp (you need a 47mm clamp, two bolts each side fits fine, £3.25 delivered from ebay) and some exhaust paste (£2.48 inc delivery from eBay versus £4 at Halfords).

I jacked the car up with the jack from the boot. Just enough room to work. The nut on the old clamp had rusted so much it was round (it's a 58 reg 6 year old car). Had to cut the old clamp off with an angle grinder. Managed to take a nick off the front pipe, 1mm more and would be trouble - this is not easy. Took a real bang with the hammer to get the rear pipe off the front pipe.

The two rubber hangers at the back would not budge at all, so cut the old exhaust off with the angle grinder which gave me enough room to really pull and get them off. There was still 1mm of rust inside the rubbers that was welded on and needed working off with a screw driver. The new exhaust went on really quickly on the rubber hangers but the clamp was another story. The Klarius exhaust has a lip about 2mm bigger than the lip on the Toyota front pipe, so took ages to get it in just the right place when tightening it. It tightened in to place fine though.

On a run the Klarius exhaust sounds a little bit more rorty and raspy but I like that, it sounds sporty, so would recommend it for the price. About £88 incl fitting was quoted to me so the saving is worth it if you are reasonable competent, but had a pain in the neck that night and stiffness the next day though. If I can get the exhaust inc delivery for £31.80 the big exhaust fitters must buy them really cheaply in bulk, so what a good margin they must be making.